Butcher shops and supermarket meat counters usually contain several roasts cut from pork shoulders and beef chuck, but the corresponding shoulder portions of lamb are relatively hard to find. The whole or "square-cut" shoulder, so-called for its squared-off shape, has a lot in common with its pork and beef counterparts. It's relatively tough and interleaved with lots of fat and gristle, so it's not the best choice for ordinary roasting. However, when it's slow-cooked, all those faults become virtues. The shoulder develops a lush, rich and tender texture as the fat and connective tissues melt away.
Trim any excess fat from the outside of the roast with a sharp knife, then use a clean paper towel to wipe away any bone fragments left behind by the butcher.
Heat a heavy skillet or Dutch oven on your stovetop, then add a tablespoon of oil. Sear the top and sides of the roast to a deep brown, which helps develop the lamb's savory flavors.
Season the lamb generously on all sides with salt and pepper, then add other flavorings such as garlic and rosemary if desired. Preheat your oven to 325 degrees Fahrenheit.
Place the lamb roast on the rack of your roasting pan, and slide it into the oven. Slow-roast the shoulder for 2 to 3 hours, until it's so tender you can easily pull off a morsel with your fork or gloved fingers.
Transfer the lamb to a serving tray and cover it loosely with foil. Let it rest for 10 to 15 minutes before carving and serving it.
Heat a large Dutch oven or heavy-duty casserole dish on the stovetop. Add 1/2 tablespoon of oil, and brown the lamb shoulder on all sides.
Remove the lamb from your pan, and add coarsely chopped onion, celery and carrot. Stir them in the hot fat until they're browned as well, then drain off any excess fat.
Season the lamb roast with salt and pepper, or other ingredients as desired. Rest it on top of the browned vegetables. Pour in enough broth or red wine to come halfway up the sides of the roast.
Preheat your oven to 325 F. Place the lid on your casserole dish or Dutch oven, and slide it into the middle of your oven. Bake the lamb shoulder for approximately 3 to 4 hours, turning it midway through the cooking time, until it's tender enough to cut with a fork.
Remove the lamb from your casserole or Dutch oven and transfer it to a serving tray. Cover it loosely with aluminum foil and let it rest for 10 to 15 minutes, while you strain the cooking liquid and thicken it to make a sauce. Serve the lamb and sauce together with your choice of side dishes.